Status of KK femtoscopy in ALICE (Based on Alice Week presentation)
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K.Mikhaylov, A.Stavinsky ITEP STAR Meeting, Dubna 11June2008 1
Status of KK femtoscopy in ALICE(Based on Alice Week presentation)
Konstantin Mikhaylov and Alexey Stavinskiy
ITEP, Russia
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Outline
K.Mikhaylov, A.Stavinsky ITEP STAR Meeting, Dubna 11June2008 2
Physics Motivation of KK femtoscopy Experimental results Distortions of K+K+ correlation function: - PID's of Kaons
- Pair PID
- Splitting-merging
- Resonances ( vτ ≥ source size): K*, Φ First results for K+K- Conclusion
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Physics motivation
Measured space-time extent of the particle emitting region for KK is pure than for ππ.
Kaon femtoscopy signal is cleaner than pion femtoscopy signal since Kaons are less affected by resonance decay.
The mT dependence: m
T(KK) > m
T(ππ).
The strangeness distillation mechanism could lead to strong temporal emission asymmetries between kaons and anti-kaons [S.Soff et al., J.Phys.G23,2095(1997);D.Ardouin et al.,Phys.Lett.B446,191(1999)].
Due to the highest branching ratio of Φ meson is KK the ΦΦ residual correlations could be seen from KK correlation function.
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Experimental results
CERN-SPS: Pb+Pb at 158 AGeV/c
RHIC-STAR: Au+Au sqrt(SNN
)=200GeV
R = 4.09 ± 0.46(stat.) ± 0.31(sys) fm andλ = 0.92±0.23(stat)±0.13(sys) at the mean transversemass <m
T> = 1.07 GeV.
[PRL,87(2001)112301]
[Phys.Rev.C 74 (2006),054902]K+K+
K0SK0
S
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The duration timeΔτ=sqrt(r2
out-r2
side)/β=
2.2± 5.2(stat.) ± 5.1(sys) fm
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Experimental results II
t
RHIC-PHENIX: Au+Au sqrt(SNN
)=200GeV
[M. Heffner J., Phys. G 30 (2004) S1043-S1047], [nucl-ex/0510014]
an approximately “universal” m
T dependence is usually
attributed to collective flow
KK one dimensional radius 3-5 fm
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ALICE Software and input
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Aliroot (with AliFemto) v4-12-Rev-02 Local analysis of 3K events PDC2007: HIJING PbPb 5.5 TeV (dN
ch/dy~6500 )
1D KK correlations0.1 < P
T < 1.0 GeV/c
Anti-splitting cutGaussian distr.: d3N/d3r*~ exp(-r*2/(4r
02))
KK r0: 2 and 5 fm
Source size for kaons from K* decay was corrected on v
K*τ
K* : r'
0=sqrt(r
02+(v
K*τ
K*)2)
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PID
K.Mikhaylov,A.Stavinsky ITEP Alice Week, CERN 31March2008 7
K
π
p
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K+ Mothers
K+direct
38% KK*(892)0
35% KK*(892)+
19% KΦ 8%,
it is two times better than π+ (π+prim
/π+all
=19%)
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π Mothers
Resonances can play significant role for ππ correlations
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Pair PID
100 events [email protected] TeV HIJING QINV
<0.25GeV/c
45%
Kdir
Kdir
7%7222( 6.95165%)
Kdir
KK*0
15298( 14.7253%)
Kdir
KK*+
7652( 7.36555%)
KK*0
KK*+
39%
8181( 7.87475%)
KK*+
KK*+
2067( 1.98962%)
KK*0
KK*0
8077( 7.77464%)
Kdir
KΦ
3129( 3.01187%)
KΦK
Φ
345( 0.332085%)
KK*0
(KK*+
)KΦ
5022( 4.83401%)
Other exotic (Kdir
KD0
,...) 1352( 1.30139%)
(KK)fake
46896( 45.1405%)
Total 103889
(100%)
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K+K+:Model&”Experiment”
Splitting cut was applied
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Source “expansion” due to K*
K
dirK
dir source size is
smaller than Kdir
KK*
due to K* decay length
Assume K* source size the same as K
dirK
dir (r
0)
Measured source in second case:
r'0 = sqrt(r
02+(vτ)2) [K
dirK
K*] or
r'0 = sqrt(r
02+(v
1τ
1)2+(v
2τ
2)2)[K
K*K
K*]
Get v of K* from generator (vτ~2.6 fm)
K
K
K*(cτ=4fm)
K
π
K
Both K are direct
One K is direct and the other one from K* decay
r0
rmeasured
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K+K+: K* source “expansion”(2fm)
Source “expansion” due to K* decay (r0=2fm, K* vτ ~ 2.6fm)
r0=2fm
r'0=2.6fm
Non Gaussian shape
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K+K+: K* “expansion” (5fm)
Source “expansion” due to K* decay (r0=5fm, K* vτ ~ 2.6fm)
r0=5fm
r'0=5.5fm
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K+K-: Model&”Experiment”
Φ → K+K-
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K+K-: K* “expansion”(2fm)
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r0=2fm
r'0=2.6fm
Non Gaussian shape
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ΦΦ residual CF in K+K-
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ΦΦ residual CF in K+K-
3000 PbPb events
Kaons only from K* decay only
Need More statistics
K0K(+/-) is better
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Conclusion
1. There are several sources of the KK correlation function “distortion”:
Single Kaon purity, Pair purity, Splitting-merging, Resonances
2. K* expansion could be important for KK
3. Study of correlated background to be continued
(fake pairs!)
4. K0SK+(-) is for ΦΦ residual correlations?
Thank you for your attention!
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Extra Slides
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K+K+:Different contribution
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K+K-: Different contribution
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With K* Correlated background!!!
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Extra Slides
Fake contribution to K+K+Good KK: 57.9429Fake KK : 42.0571pi+K+ : 27.2202pi+pi+ : 3.57522pK+ : 3.3108e+K+ : 4.3075mu+K+ : 1.12317pi+e+ : 0.999998ppi+ : 0.71421others : 0.733494